1. Field of the Invention:
The present invention relates to improved compositions of matter for restoring prepared teeth, which can be easily carved into a replica of the original anatomical form. More particularly, the present invention contemplates compositions of matter comprised of a conventional filler and a polymerizable monomeric substance having two or more polymerizable groups which react at different rates. The polymerizable substance may be comprised of a monomer having within its structure the two or more polymerizable groups, or a mixture of monomers, of different reactivity. Groups are selected having a reactivity such that the compositions will polymerize to achieve a Shore D hardness of about 85 at least in two minutes, but preferably within about twelve minutes, after reaching Shore D hardness of about 45 at 37.degree. C., thus permitting the dentist ample time to shape the restoration using conventional carving techniques.
2. Description of the Prior Art:
Dental amalgam has been used for dental restorations for over a century, and is still used in about three-fourths of all restorations. More recently developed composite restoratives comprised of a filler and a polymerizable monomer, while superior to amalgam in many respects, have replaced amalgam to only a limited extent due at least in part to the difficulty in shaping of these compositions to a replica of the original occlusal surface.
In a Class II cavity preparation, a considerable amount of the occlusal surface is involved along with at least one of the proximal surfaces. It is very important to the proper functioning of the tooth that these surfaces be restored to their original shape. The ridges and fossae of the occlusal surface have been designed by nature to form a mating surface for the opposing tooth. If the occlusion is correct, the wear rate of a restoration is limited. In a restoration which does not have the proper shape, the resulting abnormal stresses can lead to wear facets and pathological changes. Equally important is shaping the proximal surface of a restoration in order to achieve proper contact with adjacent tooth. Thus, the dentist, when placing an amalgam filling, will spend a considerable time carving and fitting the restoration. Since amalgam is easily workable for about six minutes after being packed into the tooth cavity, there is adequate time for the dentist to complete his work. On the other hand, prior art composite restorative materials have exhibited such a short time between the soft set and the hard set stage, i.e., five to thirty seconds, that the necessary hand carving and fitting is practically impossible. This disadvantage cannot be overcome by shaping of the composition after it has reached the hard set stage with the use of a drill because of difficulties in operation with extremely hard material in interproximal areas, and lack of precision.